In recent years wedge actuated brake mechanisms have been widely adopted for heavy duty vehicles such as highway and off highway heavy duty trucks and other vehicles. Examples of such brake mechanisms are illustrated in U.S. Pat. No. 3,037,548 issued June 5, 1962 to F. T. Cox et al. for "Wedge Actuated Brake Assembly" and U.S. Pat. No. 3,599,762 issued Aug. 17, 1971 to Frant T. Cox et al. for "Wedge Actuated Three-Shoe Brake." Commercial versions of brakes such as these range in size from 15 inches to 42 inches in diameter.
In wedge actuated brakes such as these, the brake shoes are forced outwardly into engagement with the associated brake drum by forcing a wedge between the adjacent ends of a pair of aligned plungers which are disposed between opposed ends of adjacent brake shoes. The wedge is free on its support to float slightly, the actuated lateral position of the wedge being determined by the resultant of the reaction forces exerted upon it by the opposed plungers.
These brakes are subjected to tremendous loads in operation due to the size of the vehicles and of the loads carried by them. This results in relatively rapid wear of the lining of the brake shoes of such brakes. As a result, it is customary to equip such brakes with a mechanism which will automatically adjust the brake actuator to accommodate for wear of the brake linings and to maintain the travel of the brake shoes and of the associated plungers between their disengaged and engaged positions substantially constant throughout the normal life of the linings. An example of such an adjustment mechanism is illustrated in U.S. Pat. No. 3,068,964 issued Dec. 18, 1962 to W. J. Williams et al. for "Automatic Brake Adjustment."
In such adjusting mechanisms one of the wedge actuated plungers for each brake shoe is a composite plunger assembly of adjustable axial length. The length of the assembly is increased automatically to accommodate for decrease in shoe lining thickness as the lining wears. This increase in length results in part from the interaction between a ratchet member that comprises part of the plunger assembly and a spring biased pawl that extends into toothed engagement with the ratchet member. As may be seen from said U.S. Pat. No. 3,068,964, such a pawl conventionally extends through a bore formed in the brake actuator housing and cooperates with an expansion spring also located in the bore and an outer plug that functions both as a reaction member for the spring and to close the housing bore against the entry of dirt and contaminants.
Any time it is necessary to disassemble the slack adjustment mechanism of U.S. Pat. No. 3,068,964 as for a maintenance inspection, it is necessary to remove the pawl from its toothed engagement with the ratchet member to free the latter for manual removal from the actuator housing. It is not unusual for such a disassembly to be necessary many times during brake actuator life. It has been found through actual experience during commercial use of such brake equipment that disassembly of the slack adjustment mechanism entails a substantial risk of loss of parts because of the removal of the pawl and associated parts. These parts are quite small and easy to misplace. In addition, when the outer plug which normally is threaded into the actuator housing is removed, the spring force often propels the plug out of the grasp of the mechanic and it may be lost. In addition, removal of the pawl itself from the actuator housing often is extremely difficult as the nature of this part requires that it be received in the bore by a close fit. It has thus been found that brake actuator parts sometimes are damaged by mechanics attempting to free the pawl member. It is important as the brake is adjusted either as above noted in the automatic form or done manually that a sealing member be provided around the plunger assembly to seal the various mechanical parts of the brake from environmental hazards as dirt, water and the like. Furthermore, when this type of brake must be dismantled for maintenance or other purposes, it would be particularly helpful if the various seals could be reused. This is particularly important when field maintenance is being done on the brake wherein the availability of such seals may be limited.
It is an object of the present invention to provide a wedge type brake having an actuator of the type described including an adjustable sealing member to seal the brake assembly from environmental hazards as the plunger assembly is moved linearly.